It’s getting hot (and dry) in here! Freshwater crayfish and their vulnerability to climate change

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There’s been much to enjoy this summer here in London – it’s been wall to wall sunshine, something which is – suffice to say – not a common occurrence in the UK.

More often than not, summer holidays are a wash out, but this year, our record-breaking summer has no doubt enticed many people to frolic in the water for some much-needed cool relief. At the same time, there has been much talk in the media about hosepipe bans, water shortages and - looking at the long-term – an increase in the frequency of extreme weather events due to the impacts of climate change.

Euastacus bindal. A very threatened species of crayfish. Photo: Diana-Angelique Virkki
Euastacus bindal. A very threatened species of crayfish.

We are not the only species to feel the impact of our changing climate. Just last week, we published our latest research on the climate change vulnerability of a group of species which has often been overlooked in the wider conservation context – and which also frolics in water: freshwater crayfish. Led by our collaborators at the University of Melbourne, we carried out the first global trait-based assessment of climate change vulnerability for this interesting group of species. This showed that 15% of crayfish are vulnerable to climate change. Which begs two questions: 1) what is a trait-based climate change vulnerability assessment, and 2) why study crayfish?

Blue crayfish
Cherax destructor
Let’s start with the trait-based climate change vulnerability assessment. This involved assessing how vulnerable crayfish are to climate change, at a global level, looking at three different aspects of climate change vulnerability: a species’ sensitivity to climate change, its capacity to adapt to changes in its environment and its actual exposure to climate change. There are several variables associated with each of these aspects. For example, a species which can only tolerate a narrow range of temperatures is more sensitive to climate change than a species with a wide temperature tolerance. A species which is surrounded by barriers which prevent it from moving away from the area, has a low ability to adapt to climate change, if their environment becomes ‘climatically’ hostile (for example, too hot, too wet or too dry). A species living in an area which is expected to see massive temperature changes in the future, is classed as having high exposure to climate change.

These are some of the examples of the variables that go into a trait-based climate change vulnerability analysis. In our crayfish study, we had seventeen such variables to consider. Species scoring high in all of these (i.e. sensitive, unadaptable and exposed species) are ranked as having high vulnerability to climate change overall.

So why crayfish? Freshwater crayfish are a diverse group of crustaceans, divided into two superfamilies: the Astacoidea (in the Northern Hemisphere) and the Parastacidae (in the Southern Hemisphere). They are economically important species, and a recent assessment of their conservation status, led by ZSL, showed that 32% of species are globally threatened. The cause of threats varied considerably within the group: for example, 47% of all Australasian species were found to be threatened with extinction, with most species at risk from climate change impacts (e.g. wild fires, drought), but also agriculture and invasive species. Most of the world’s crayfish live in North America though, especially in the southeastern United States; here, crayfish face a much greater threat from pollution, damming and urban development.

Euastacus sp crayfish in river
Euastacus sp. spotted in the Blue Mountains of Australia

Our latest results on the vulnerability of crayfish to climate change supplements our previous work on the overall conservation status of these fascinating creatures. Previously, we found that only 2% of U.S crayfish species and 6.6% of Australian species occur in protected areas. Now, we are highlighting additional significant shortfalls in conservation efforts for crayfish: for example, we highlight which species require better statutory protection against threats from exploitation and habitat modification, as these are likely to exacerbate the impacts of climate change.

More generally, this work adds to the growing evidence base that our freshwater ecosystems and the species relying on them are under increasing threat. We are currently assessing extinction risk data for freshwater molluscs (snails and mussels), which shows a similar picture of global threat. Our Living Planet Index shows an average decline in vertebrate populations by 58% since 1970, yet shows an even more dramatic decline of 81% for freshwater vertebrate populations. 

So, as you enjoy the summer, spare a thought for the humble crayfish. Most crayfish species rely on relatively unpolluted waters, and are innately sensitive to climate change, so that monitoring the fate of the world’s crayfish in these times of global change is not just important for their well-being, but also for ours. After all, we all enjoy (and need) cold clear water – not only in our current record summer.  

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